docs: def zext(self, n):
          ''' Zero-extend the variable to n bits.
          
          n bits must be stricly larger than the actual number of bits, or a
          ValueError is thrown
          '''
  
          if n <= self.nbits:
              raise ValueError("n must be > %d bits" % self.nbits)
  
          mba_ret = self.__new_mba(n)
          ret = mba_ret.from_cst(0)
          for i in range(self.nbits):
              ret.vec[i] = self.vec[i]
          return mba_ret.from_vec(ret)